This research proposes to develop a new radiocontrast agent, highly selective for X-ray visualization of cartilage. For this objective we wish to synthesize several types of new compounds; iodine-bearing aryl bis-quaternary amines. The choice of the bis-quaternary amine structure is based on the fact that hexamethonium and decamethonium distribute and bind selectively and persistently to cartilage, but not to bone. The several types of new compounds to be synthesized will be investigated for their ability to achieve radiopacity in cartilage, in-vitro, and by parenteral and intra-articular injection in intact animals (mice, cats, dogs, primates). In the coming year, chemical synthesis will also be directed to developing radioactively labelled compounds to be tested for applicability to clinical radioscanning techniques. Aryl bis-quaternary amines bearing I125 or I131 will be the first approach. A second series of compounds will be aliphatic bis-quaternary amines with chelating functional groups, capable of forming complexes with 99mTc. A radiocontrast agent selectively bound to cartilage would have potentially great significance in clinical diagnostic radiology for the examination of joint tissues and intervertebral discs in disease states and trauma.